Fine Structure of Transition and Maturation Zones in the Enamel Organ of the Kitten. One week old kittens are fixed by vascular perfusion. Tooth germs are decalcified before further processing. The ameloblast fine structure is correlated with the functional aspects -both established and hypothetical - of transition and enamel maturation, such as the end of enamel deposition, deposition of a cuticle, matrix reduction, and others. Movement and Absorption of Horseradish Peroxidase (HRP) in the Rat Incisor Enamel Organ. HRP is injected into adult rats. The rats are killed at appropriate time intervals, and the fine structure distribution of HRP is studied after visualization by a histochemical reaction. This procedure will reveal flow patterns of extracellular fluid within the enamel organ, compartmentalization of the extracellular spaces, and resorptive activities of ameloblasts and other enamel organ cells. Distribution of Acid Phosphatase Activity in the Enamel Organ of Rat Incisor. Acid phosphatase activity is related to phagocytosis by enamel organ cells and is thought to play an important role in mechanisms of calcification. It will be attempted to achieve an improved demonstration of enzyme activity by adapting a perfusion technique.